WASHINGTON -- NATO leaders meet this week for a summit commemorating the 75th anniversary of the military alliance, which has never been larger and more focused but is also facing potentially existential threats from outside and within.

If Russia鈥檚 war in Ukraine, challenges posed by an increasingly aggressive China, and the Israel-Hamas conflict in Gaza weren鈥檛 enough, some key members' commitment to defend their allies is coming under question.

There is deep uncertainty over President Joe Biden鈥檚 ability to beat his predecessor, NATO skeptic Donald Trump, in November to lead the most powerful member of the alliance.

While Biden鈥檚 political troubles are stirring concerns at home and abroad, countries in Europe are facing their own issues with a rise of far-right populism, particularly in France and Hungary, threatening what had been a bedrock pillar of post-World War II security and stability.

Here鈥檚 what to watch for at the three-day summit:

All eyes on Biden

Reeling from his disastrous June 27 debate performance and struggling to hold his reelection campaign together, Biden says people should look to his interactions at the NATO summit for proof that he is still strong and vigorous enough to lead.

Diplomats and analysts say they will be watching closely 鈥 although NATO leaders accept they have no control over American elections and are unlikely to weigh in publicly.

鈥淭he outcome of the November election matters enormously for NATO and pretty much all heads of state and government in the alliance feel the same way, even if they refuse to discuss it,鈥 said Jeff Rathke, president of the American-German Institute at Johns Hopkins University.

The prospect of Trump returning to the White House has alarmed many in Europe who fear he may reduce U.S. commitments to NATO or Ukraine 鈥 or pull them completely.

鈥淭here is nothing that Biden鈥檚 NATO counterparts can do to affect that outcome, so they are in the uncomfortable position of being observers to a process that is critical to the alliance but over which they have no control,鈥 Rathke said.

Biden, who has taken credit for strengthening NATO and resisting Russian President Vladimir Putin, said his confidence and competence would be on display.

But he will be under tremendous pressure to quell growing concern that he is not up to the job, as either de facto head of NATO or commander in chief of the alliance鈥檚 most important member.

鈥淭he unpredictability of what (Trump) might do and how quickly in office he might do it, leaves people on edge,鈥 Rathke said. 鈥淚t would be a significant jolt to NATO if he were to win.鈥

But it's also not all about Joe

As much as the spotlight will be on Biden, 31 other leaders have a voice in NATO decision-making. The summit will be British Prime Minister Keir Starmer鈥檚 first appearance on the world stage just days after winning a resounding victory in elections.

Although Starmer has signaled continued strong support for both NATO and Ukraine, gains made by far-right parties, as well as left-wing groups opposed to Western support for Israel鈥檚 war in Gaza, may dilute London鈥檚 influence.

Of more concern is turmoil in France, where President Emmanuel Macron's government is facing political uncertainty after left-wing parties united to beat a surging far right in legislative elections but still didn't win a majority in parliament. The far-right party, which is skeptical of NATO, greatly increased the number of seats it holds.

And there are Hungary and Turkey, the last two NATO members to hold out on allowing the newest members, Finland and Sweden, to join the alliance. Viktor Orban of Hungary raised alarm bells by visiting Russia last week for talks with Putin, and Turkey鈥檚 Recep Tayyip Erdogan remains on good terms with the Kremlin.

NATO's future

In many respects, the alliance has never looked stronger. Since Russia鈥檚 2022 invasion of Ukraine, NATO gained those two members, bringing the total to 32. At the same time, Eastern and Central European members closer to Russia鈥檚 borders 鈥 the Baltic states, Poland and the Czech Republic 鈥 have stepped up support for Ukraine and NATO as an institution.

But NATO is fragile. Its policies must be made by unanimous consensus, and political upheaval in capitals hinders future decision-making. NATO leaders are expected once again to reaffirm their 鈥渙pen door鈥 policy 鈥 that membership is open to any country meeting the requirements. But Ukraine won't see its hoped-for invitation this week.

鈥淚n some ways, this NATO summit is coming as sort of the best of times and the worst of times. The best of times, in the sense that the alliance knows what it鈥檚 about,鈥 said Max Bergmann, director of the Europe, Russia, and Eurasia program at the Center for Strategic and International Studies.

鈥淏ut it鈥檚 also sort of the worst of times 鈥 obviously because of the war in Ukraine, challenges of ramping up European defense spending, concerns about the reliability of the United States,鈥 he said.

Defense spending has been one of Trump鈥檚 biggest complaints about NATO, and he has repeatedly suggested that the U.S. wouldn't defend countries that don鈥檛 meet the agreed-upon goal of spending two per cent of gross domestic product on defense.

NATO officials have championed a significant increase 鈥 to 23 鈥 in the number of allies meeting that commitment. Several more are expected to say they're meeting that standard during the summit.

Keeping up support for Ukraine

Many NATO allies in the past year have signed their own security agreements with Ukraine to provide long-term guarantees of assistance for Kyiv to defend itself from Russia and prevent possible future attacks.

Russia made significant battlefield gains over the past several months during congressional delays in approving U.S. military aid. Those have been overcome, and a new multibillion-dollar package is expected to be announced this week.

But Ukraine鈥檚 goal is joining NATO, placing it under the alliance鈥檚 Article 5 collective security umbrella that obligates other members to come to its defense if attacked.

Membership is highly unlikely while the conflict rages. However, the allies plan to present Ukraine with a 鈥渂ridge鈥 to membership that would further lay out next steps.

In the meantime, countries are expected to pledge new military and economic support. Billions of dollars have already been sent to Ukraine, and officials say more is coming. Outgoing NATO Secretary-General Jens Stoltenberg said Friday that contributions of roughly US$43 billion per year should be the baseline moving ahead.

Don't forget about China

NATO allies also are focused on threats posed by China, including persistent disinformation campaigns aimed at sowing doubts in democratic systems. And they have repeatedly complained that Chinese sales of some tools and technology have allowed Moscow to rebuild Russia鈥檚 defense industrial base to wage war in Ukraine.

The U.S., in particular, has called out China for pursuing policies that threaten European security as Beijing seeks broader commercial relations with the countries of Europe.

For the third year in a row, leaders or top officials from Australia, New Zealand, Japan and South Korea will attend the NATO summit for discussions on how to deal with Chinese threats in the South China Sea and beyond.